Carrier Condensing Unit Not Running

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Old 03-01-13, 12:27 PM
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Carrier Condensing Unit Not Running

Single family home built 1977
Carrier Central HVAC 6 years old

Hey guys, I'm no HVAC tech or electrician, so I'm hoping to get a little guidance here. I moved into this house a few months ago, and the HVAC system worked fine for inspection. Because of the cooler weather, we haven't tried running the A/C until now. The handler is functioning and blowing air, but the condensing unit is not running. Neither the fan or compressor as far as I can tell, no noise whatsoever coming from the unit. I read a few posts without doing enough research and replaced the contactor and capacitor myself and it did nothing. What I did not test was the voltage of signal going to the contactor from inside. The condensing unit runs if I have the power (breakers) on and manually depress the contactor. I then did more searching and checked voltage for the signal wire (yellow/blue and brown/yellow?) and when the thermostat sends the signal, I'm only getting .14V to the contactor, obviously not enough for it to engage. Now I'm not sure where to go/test next. I have a multimeter but not a vast knowledge of electrical diagnostics.

I have 120V+ on each terminal on both sides of the contactor (should it ALWAYS read 240V on the other side like it does?) all the time, 120V+ on each terminal of the capacitor.

There is a 'PING' noise in the condensing unit when the signal is sent, not sure where that's coming from but that's all that happens. Again, it now has a new capacitor and contactor but the problem seems to be not receiving the correct voltage from the signal wire. I've attached a picture of the wiring, did I check the right 'signal wires' for voltage? What is next?
 
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Old 03-01-13, 05:36 PM
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Welcome to the forums.

We'll help you out.

When checking for voltage....measuring from one leg to ground and seeing 120 vac is ok.....but you really need to see 240 vac on the line side of the contactor.

You pushed in the contactor and the compressor and the condensor fan both ran... correct ?

I'll assume yes and that would also confirm that you have 240vac. That contactor requires 24 vac to close on its own.

One reason it wont close is that there are safety switches in series with it. So if one of those safety switches is open the contactor wont close.

The usual cause of the contactor not closing, assuming the thermostat is ok, is the low pressure safety switch is open. This switch needs to see a minimum freon pressure to close. It does this so that the compressor wont run on a low charge.

I'm not familiar enough with your unit to give you internal wiring colors but if you look under the fan in the area where the compressor is.....you'll see copper lines. The safety switches will be installed in those lines.

With the power OFF at the compressor end and at the air handler end ...... you can check those with an ohmmeter. They should show a short.

The regular HVAC guy will be stopping by and he would know exactly what to check.
 
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Old 03-01-13, 05:51 PM
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Thanks for the response. That is what I am looking for, the reasons I wouldn't be getting the correct voltage to close the contactor. The thermostat isn't very old, I'm assuming it is 6 years old along with the HVAC system. I do believe both the fan and compressor were running, I could hear the buzzing/humming of what I believe the compressor should make. I can certainly check the safety switches tomorrow, maybe there are a few other things I can check too? I know the wiring from the house goes to the circuit board before the contactor. Just not sure what it talks to between that time. Again thanks, that's another thing I did not know to check.
 
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Old 03-01-13, 05:59 PM
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I see five orange wire nuts in the bottom of the unit. That tells me that the system is more involved than a standard compressor unit since there are five wires connecting it to the inside unit. Possibly a heat pump system. If yes then the system is a little more involved with a defrost control board.

If you can post the model number of the condensor I could check for a wiring diagram.
 
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Old 03-01-13, 06:34 PM
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Model # 25HBR330A300 I believe is what you need? There are two model #'s listed on the handler in the attic and I think that is the right one...
 
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Old 03-01-13, 07:40 PM
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On the wires coming outside (orange wire nuts)......when calling for air you should see 24 vac on C (black) and Y (yellow)

If you have that then there are three safety switches in line:
LPS - low pressure switch - yellow wires
DTS - discharge temp switch - red wires
HPS - high pressure swith - blue and yellow or blue

Check across the LPS switch for continuity. If it shows open.....no meter movement.... you need recharge.

This is the link to your unit
http://www.docs.hvacpartners.com/idc.../25hbr3-1w.pdf
 
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Old 03-28-13, 07:26 PM
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Thank you for the help, unfortunately I did not have the time to look at it since previously mentioned. I had a friend look at the unit tonight and he says it's a bad defrost control board.

At first there was no 24V from inside to the condensing unit, and we found a broken wire in the exterior wall where the installers had made a splice in the wires. Re-connected that and got 24V at the unit on the signal wire (yellow), but not out of the control board and to the contactor. Where are the sensors? I am not sure how he determined it was the control board (I wasn't by his side the whole time). He is an HVAC tech, so I trust his word but I don't recall him mentioning any sensors being 'ok' and I forgot about it until now. If it is the control board, I would probably have to get that at the local supply house? It doesn't look like Grainger carries that. Only problem is I only have tomorrow until I head out of town again.

Carrier Defrost Control Board HK32EA001.
 
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Old 03-28-13, 08:01 PM
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Put the part number in Google. It will come up for sale all over the internet. Runs around 100.00

With that number you should be able to get it at a local HVAC parts place near you. Check the phone book.
 
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Old 03-29-13, 08:14 PM
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PJmax, you were absolutely right. The reason the condensing unit wasn't kicking on was due to (well, after fixing the 24V broken wire) the LPS. Turns out my unit is leakage freon somewhere. In small increments but worsens when the heat is used. My friend is coming back next week with his 'sniffer' to find and fix the leak (tried the spray and bubble method, no luck). Then we should be good to go, no expensive parts. Thanks again and I will update when the unit is 100% again.
 
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Old 03-29-13, 08:54 PM
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Yeah.......if the spray and bubbles actually showed you a leak the system would be empty.

Hopefully the sniffer should find it.
 
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Old 03-30-13, 08:11 AM
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The leak could be in the indoor coil.

Copper + aluminum + water + VOCs (indoor air pollution) = corrosion
 
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